1. Field of the Invention
This invention relates to a wire fastening tool for fastening a wire, and particularly to the structure of a fastening tool suitable for fastening the opposite ends of a metallic wire when supporting and fixing fractured bone portions or re-fixing broken bones.
2. Related Background Art
Heretofore, when fractured bone portions are to be tied together or when after a portion of a bone was cut off for some reason or other, the cut-off portion is to be again fixed at its original position, it has been the practice to pass a wire for a living body through an insertion hole formed in the bone or put a wire for a living body around the body to thereby bind up the wire, and fasten the opposite ends of this wire to thereby fix the broken-away portion of the bone. The fastening of the wire is accomplished by once tying up the wire tightly, and then wrenching the opposite ends of the wire together.
As the wire for a living body, use is often made of a single wire of stainless steel, Co--Cr--Mo alloy or the like. However, these wires have suffered from problems in terms of corrosion resistance and fitness to a living body and moreover, have had a disadvantage that when MRI (magnetic resonance image pickup method) is used, image pickup is hampered by the halation caused by the wire.
On the other hand, in recent years, use has also been made of wires of pure titanium or titanium alloys having good corrosion resistance and good fitness to a living body. These wires have a feature that they do not cause halation to an electromagnetic wave and moreover, when they are used with artificial bones or artificial dental roots made of titanium or a titanium alloy which have recently used, the wires used are the same metal as these and therefore, electrochemical corrosion occurring between different metals can be avoided.
However, the wires of titanium, as compared, for example, with wires of stainless steel, merely have a fraction of ductility and a little over half of tensile strength and therefore, unless the wire fastening work is done carefully, the wrenched-together portions of the wires may be broken away. Accordingly, there have been cases where during a surgical operation, sufficient tying-up or wrenching together cannot be done from the fear against the breakage of the wire and precise fixing of bone tissue cannot be accomplished.
So, for example, in Japanese Laid-Open Patent Application No. 4-156837, it is described to insert two wires into a metal fitting of titanium having a U-shaped or otherwise shaped opening, and caulk and fix the metal fitting and the wires. According to this metal fitting, the wires need not be tightly wrenched together and thus, the possibility of the wires being broken away can be reduced.
However, said metal fitting is formed into a channel of U-shaped, V-shaped or otherwise shaped cross-section provided with a wire insertion opening, and this leads to a problem that the wires cannot be sufficiently supported when the wires are tied up while being inserted in the metal fitting.
Also, a plurality of wires are simply caulked and fixed and therefore, to obtain a sufficient fastening force, it is necessary to partially strongly press the metal fitting to such a degree that a recess is formed in the outer surface portion of the metal fitting, and to a cause the wires to eat into the metal fitting with the inner surface of the metal fitting and the wires deformed into an uneven shape. Accordingly, the strength of the caulking must be suitably adjusted, and if the caulking is weak, the fastened portion may come off, and if the Caulking is too strong, the wires may be broken away.